Yet another way that phage λ manipulates its E scherichia coli host: λ rexB is involved in the lysogenic–lytic switch

Summary The life cycle of phage λ has been studied extensively. Of particular interest has been the process leading to the decision of the phage to switch from lysogenic to lytic cycle. The principal participant in this process is the λc I repressor, which is cleaved under conditions of DNA damage. Cleaved λc I no longer acts as a repressor, allowing phage λ to switch from its lysogenic to lytic cycle. The well‐known mechanism responsible for λc I cleavage is the SOS response. We have recently reported that the E scherichia coli toxin‐antitoxin mazEF pathway inhibits the SOS response; in fact, the SOS response is permitted only in E . coli strains deficient in the expression of the mazEF pathway. Moreover, in strains lysogenic for prophage λ, the SOS response is enabled by the presence of λ rexB . λ RexB had previously been found to inhibit the degradation of the antitoxin MazE , thereby preventing the toxic action of MazF . Thus, phage λ rexB gene not only safeguards the prophage state by preventing death of its E . coli host but is also indirectly involved in the lysogenic–lytic switch.